The present invention relates to a photo electric measuring system for detecting relative movements of two components in a Moire strip system.
It is known that electrical signals produced from measuring the relative positions of two optical grids contain harmonics. For example, German unexamined patent specification DE-OS No. 2500798 discloses a Moire stripe detector containing four partial fields. The partial fields are arranged such that straight lines which pass through the surface centers of gravity of the respective partial fields run parallel to the Moire stripes as well as parallel to each other. According to one of the examples, a better harmonic filtering is achieved than in the other examples.
Currently, in order to eliminate harmonic components from an electrical output signal, very expensive apparatus is required. For example, additional components such as shaped diaphragms are to be avoided. (See German Pat. Nos. 1,673,988 and 1,941,731.) In addition, the measuring arrangements must be insensitive to inaccuracies in the graduations employed.
It is therefore an object of the present invention to provide a photoelectric measuring system which eliminates harmonic components from an electric signal produced by an optical measuring system. It is further an object of the present invention to provide a photoelectric measuring system which will inexpensively eliminate harmonic signals generated while measuring Moire stripes. Other objects of the present invention will be apparent to those skilled in the art in view of the specification and claims.